A number of systems for converting sunlight to electricity are known. One such system that has proven useful in efficiently producing electricity from the sun's radiation is described in U.S. Pat. No. 4,691,076. In that system, an array is formed of semiconductor particles or spheres. Each sphere has a p-type interior and an n-type skin. A plurality of the spheres are held in a matrix which includes a pair of aluminum foil members which form the contacts to the p-type and n-type regions. The foils are electrically insulated from one another and are flexible. Multiple flexible and conformable arrays can be electrically interconnected to form a module of solar cell elements for converting sunlight or other forms of photon energy into electricity.
In order to produce sufficient quantities of reasonably priced arrays, it is necessary to utilize a process for their manufacture that is uncomplicated, low cost and efficient. An uncomplicated system would be one using currently available technology in such a way that the applicable process steps can be conducted in a highly repeatable manner. Moreover, the less complicated the process steps, generally, the more cost effective will the entire process be carried out. Finally, the more repeatable the process, the more efficiently the operation and the higher the production of solar arrays.
A key process step in the making of silicon solar cells is affixing the silicon spheres to the foil matrix. A known technique for bonding silicon spheres to an aluminum foil is to heat the foil to a temperature slightly below the eutectic point (approximately 570.degree. C.) and then press (or push or drive) the spheres into the foil by using a free falling weight. The free falling weight generates sufficient shearing forces at the silicon and aluminum foil interface to form good adhering bonds.
Drop weight bonding has numerous problems and disadvantages. First, the technique is inherently slow. Second, the drop weight approach does not lend itself to scaling up for larger production volumes. Another problem with drop weight bonding is that distortions in the impact surface of the weight result in undesirable center pressures. Finally, the technique results in too many damaged spheres and shorted cells.
Another method for affixing silicon spheres to a foil matrix is described in U.S. Pat. No. 5,091,319. In that patent, the silicon spheres are pressed into undersized apertures formed through one foil of the foil matrix using a hydraulic press. This method, however, suffers from the deficiency that the spheres throughout the cell are not always uniformly bonded to the aperture walls, especially for larger sized cells.